Low cost multilayer elastomeric films having a low permanent set

ABSTRACT

The presently described technology provides a low cost multilayer elastomeric film containing at least one layer of styrene block copolymer and at least one elastomer layer substantially free of styrene block copolymer such that the resultant film has a low permanent set substantially equal to or less than a film comprised of styrene block copolymer only. The elastomeric film may be used in elasticized features of various articles, such as disposable absorbent articles. Methods for producing the low cost elastomeric film having a low permanent set are also described.

RELATED APPLICATIONS

This application is a divisional application of U.S. Pat. No. 7,629,278issued on Dec. 8, 2009, which is related to, and claims benefit of andpriority from, Provisional Application Ser. No. 60/692,308 filed on Jun.20, 2005 (Attorney Docket No. 2308-16794US01), titled “Low CostMultilayer Elastomeric Films Having A Low Permanent Set”, the completesubject matter of which is incorporated herein by reference in itsentirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

BACKGROUND OF THE INVENTION

The presently described technology relates generally to the art ofpolymer films, and more specifically to multilayer elastomeric filmscontaining styrene block copolymer(s) (“SBC”) and a second non-SBCelastomer or plastomer, which exhibit improved film properties incomparison to films comprised of SBC only.

Disposable absorbent articles (e.g., disposable diapers for children oradults) often include elastic features designed to provide enhanced andsustainable comfort and fit to the wearer by conformably fitting to thewearer over time. Examples of such elastic features may include, forexample, elastic waist features, elastic leg cuffs, elastic side tabs,or elastic side panels that can provide expansion and contractionbenefits to an absorbent article so that the article may conform to thewearer in varying directions. Additionally, such elastic features areoften required to be breathable to provide a desired level of comfort tothe wearer's skin.

Further, the elastic features of disposable absorbent articles may bemade of compound materials comprising elastic films (includingbreathable films) or elastic scrims, laminated to non-woven fabricsproviding desired surface properties and aesthetics of the compoundmaterial. The elastic properties of such compound materials are oftenobtained by activating the elastic properties within the compound, whichcan be latent before activation, that is the compound material which isnon-elastic by itself before the activation becomes elastic after theactivation as it were itself elastic.

One of the activation techniques can include mechanical stretching, inparticular incremental mechanical stretching. Such mechanical stretchingprovides permanent elongation of the non-woven substrate(s) comprisingthe compound material to enable the elastic member(s) of the samecompound material (e.g., elastic film or elastic scrim) to stretch undera tension force applied thereto. When the elastic member is allowed tocontract, the permanently elongated nonwoven fabric wrinkles or shirrsto contract in at least one dimension along with the elastic member. Indoing so, the compound material becomes elastic or an elasticizedmaterial.

However, the elasticized materials are often expensive because theycannot only include inexpensive elastic materials, but also requiredifficult processing and handling of elastic members (i.e., elasticfilms and scrims). Such processing can include additional and expensivecutting and slip steps or procedures. Thus, because the elasticizedfeatures are relatively expensive to produce and include, they typicallycontribute to a higher cost of various articles produced (i.e.,absorbent articles containing such elasticized members).

Another method of allegedly enhancing fit and comfort to an absorbentarticle is to use elastic strands in its construction. Published UnitedStates Application No. 2003/0089454 to Johnson, describes methods forthe manufacture of absorbent articles utilizing such elastic strips.Although the reference describes the articles as providing a comfortableand contoured fit to the wearer over time, the construction of sucharticles with elastic strips often results in a bulky side area of theproduct.

Moreover, elastic strand products and other elasticized materials areoften expensive to produce because of the inclusion of expensiveelastomeric materials such as a styrene block copolymer, but alsorequire difficult process operations.

There is market interest based upon aesthetic and economic reasons inreplacing the Lycra® or styrene block copolymer elastic strands usedtoday with an elastic film. By incorporating an elastic film rather thanLycra® or styrene block copolymer elastic strands it is believed thatthe absorbent product would exhibit a flatter-looking side panel.Further, using a single roll of elastic film could eliminate theprocessing problems inherent with handling many spools of elasticstrands. Further, elastic films may not be generally a more costeffective alternative to Lycra® elastic materials.

Thus, there is a need for a low cost multilayer elastomeric film havingimproved tear strength, and elongation to break, while providing a highelastic recovery, as measured by the permanent set, more typical of anSBC elastomeric film.

BRIEF SUMMARY OF THE INVENTION

In light of the problems, difficulties and undesired outcomes describedabove, a new low cost elastomeric film having a low permanent set foruse in elasticized features of various articles, for example disposableabsorbent articles, has been discovered. Methods and products resultantfrom such methods for producing the new low cost elastomeric film havinga low permanent set are also described herein.

More specifically, the presently described technology involveselastomeric films, preferably multilayer elastomeric films, containingat least one layer of styrene block copolymer (SBC) and at least oneelastomer or plastomer layer substantially free of styrene blockcopolymer.

Thus in one aspect, the present technology concerns an elastomericcomposition containing at least one styrene block copolymer and at leastone elastomer or plastomer which is substantially free of styrene blockcopolymer such that the resultant elastomeric composition has apermanent set substantially equal to or less than an elastomericcomposition containing only styrene block copolymer.

In another aspect of the present technology there is provided apolymeric coextruded multilayer film or a multilayer film laminatehaving at least one layer comprised of a styrene block copolymer and atleast one layer consisting essentially of an elastomer or plastomersubstantially free of styrene block copolymer. The resultant polymericcoextruded multilayer film or multilayer film laminate has a permanentset substantially equal to or less than a coextruded multilayer film ormultilayer film laminate composed of only styrene block copolymer.

A further aspect of the presently described technology also concerns amethod of manufacturing a multilayer elastomeric film by coextruding atleast one styrene block copolymer layer with at least one elastomer orplastomer layer substantially free of styrene block copolymer, such thatthe resultant multilayer elastomeric film has a permanent setsubstantially equal to or less than that of a coextruded multilayerelastomeric film containing one or more layers of styrene blockcopolymer only.

In yet a further aspect of the present technology there is provided amethod of manufacturing a multilayer elastomeric film laminate bylaminating at least one styrene block copolymer layer with at least oneelastomer or plastomer layer, wherein the resultant multilayerelastomeric film laminate has a permanent set substantially equal to orless than that of a multilayer elastomeric film laminate containing onlyone or more layers of styrene block copolymer.

A still further aspect of the present technology concerns an absorbentarticle comprised of a component (for example, a side tab, a side panel,or a waistband) that has at least one non-woven outer layer and at leastone elastomeric film inner layer attached to the non-woven outer layer,and the elastomeric film inner layer is comprised of at least one layerof a styrene block copolymer and at least one layer consistingessentially of an elastomer or plastomer. Additionally, the elastomericfilm inner layer has a permanent set substantially equal to or less thanan elastomeric film inner layer of an absorbent article comprised onlyof styrene block copolymer.

Moreover, another aspect of the present technology concerns a multilayerelastomeric film having a formulation in each layer. Preferably, in atleast one embodiment of the presently described technology there isprovided at least one core layer containing between about 1% to about100%, more preferably about 50% or greater by weight of a styrene blockcopolymer; at least one inner layer comprised of between about 0% toabout 100%, more preferably about 50% or greater, and most preferablyabout 80% or greater by weight of a ethylene/propylene copolymer,propylene copolymer or combinations thereof that is positioned on atleast one side of the core layer; and at least one outer layer comprisedof between about 0% to about 100%, more preferably about 50% or greater,and most preferably about 80% or greater by weight of a high or lowdensity polyethylene (or combinations thereof) that is positioned on atleast one side of the inner layer. The resultant multilayer elastomericfilm has a permanent set substantially equal to or less than thepermanent set of a multilayer elastomeric film consisting only ofstyrene block copolymer.

In yet a further aspect of the present technology, there is provided anelastomeric film having at least one skin layer (which may comprise oneor more inner layers and one or more outer layers in relation to a corelayer) and at least one core layer which further comprises at least onestyrene block copolymer and at least one elastomer or plastomer layerwhich is substantially free of styrene block copolymer. The layer ratiosof the described film are generally from about 20% to about 80%, morepreferably 30% to about 75%, most preferably from about 35% to about 65%for the core layer and from about 0% to about 40%, more preferably about15% to about 35% for each of the inner layers, and from about 0% toabout 35%, more preferably less than about 20% for each of the outerlayers (which may act as a skin layer). The resultant elastomeric filmhas a permanent set substantially equal to or less than an elastomericfilm containing only styrene block copolymer.

In all of the aspects of the present technology described above, theelastomeric films, laminates, articles and the like have improvedproperties over conventional elastomeric films comprised of only SBC.The addition of the elastomer or plastomer layer or layers as describedherein improves the tear strength and elongation to break of theelastomeric films of the present technology, while providing a highelastic recovery, as measured by the permanent set, more typical of anSBC elastomeric film. Surprisingly, it has been found that theelastomeric films of the presently described technology have a permanentset substantially equal to or less than an elastomeric film containingone or more layers of SBC alone. As a result, the elastomeric films,laminates, and articles of the present technology offer a low costalternative to more expensive elastomeric films currently available.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS AND/OR FIGURES

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter, which is regarded as thepresently described technology of the present invention, it is believedthat the presently described technology will be more fully understoodfrom the following description taken in conjunction with theaccompanying figures, in which:

FIG. 1 is a graphical illustration of a first hysteresis curve,“activation curve” for a styrene block copolymer and anethylene/propylene copolymer.

FIG. 2 is a graphical illustration of a series of second loading curvesfor styrene block copolymers and ethylene/propylene copolymers atvarious gauges.

FIG. 3 is a graphical illustration of a second cycle hysteresis curvefor styrene block copolymers.

FIG. 4 is a graphical illustration of a second cycle hysteresis curvefor ethylene/propylene copolymers.

FIG. 5 is a graphical illustration of the effect of skin resin type onsecond cycle hysteresis curve for an elastomeric film.

FIG. 6 is a graphical illustration of second cycle permanent set as afunction of film thickness and skin layer percent.

FIG. 7 is a graphical illustration of the effect of skin layer percenton second cycle loading curve for an elastomer.

FIG. 8 is a graphical illustration of second cycle hysteresis comparisonof films with coextruded elastic cores and films with single elasticresin cores.

FIG. 9 is a graphical illustration of the permanent set comparison of afilm with a coextruded elastic core and films with single elastic resincores.

FIG. 10 is a graphical illustration of a tensile elongation to breakcomparison of a film with a coextruded elastic core and films withsingle elastic resin cores.

FIG. 11 is a graphical illustration of an Elmendorf Tear comparison of afilm with a coextruded elastic core and films with single elastic resincores.

DETAILED DESCRIPTION OF THE INVENTION

The elastomeric films, methods of producing such films and articlesincorporating the elastomeric films of the presently describedtechnology are suited for a variety of uses and applications, inparticular for use in or as garments, such as a disposable absorbentarticle.

As used herein, the term “absorbent article” refers to a device whichabsorbs and contains body exudates, and more specifically, refers to adevice which is placed against the skin of a wearer to absorb andcontain the various exudates discharged from the body. Examples ofabsorbent articles include diapers, pull-on pants, training pants,incontinence briefs, diaper holders, feminine hygiene garments, and thelike.

The term “elastic” or “elastic engine” refers herein to any materialthat upon application of a force to its relaxed, initial length canstretch or elongate to its elongated length without rupture andbreakage, and which can substantially recover its initial length uponrelease of the applied force.

The phrase “substantially equal” herein refers to any numerical valuewith a variance of (+) or (−) about 20% from the base numerical value.Thus, one of ordinary skill in the art will recognize that the physicalproperty values (or other values) set forth herein, in particular,permanent set, are capable of being within the spirit and scope of thepresent technology after consideration of test method error.

The term “elasticized” refers herein to any elastic material comprisingone or more elastic components and one or more nonwoven fabrics, whichmay be activated to provide permanent elongation of the non-wovenfabrics to enable the elastic components to stretch under application ofa tension force. Additionally, the term “elasticized” can also referherein to nonwovens that are inherently elastic, but do not requireactivation. However, such nonwovens are expensive to manufacture.Further the term “elasticized” can also refer herein to nonwovens thatare inherently extensible, but do not recover. Such nonwovens can alsobe made to behave in an elastic manner by laminating them to elasticfilms. Thus, one of ordinary skill in the art will appreciate that theterm “elasticized” can refer to any of the various activated,non-activated, laminated, and inherent elastic compounds and situationsnoted above.

The term “latent elastic material” refers herein to a compound materialwhich by itself can be substantially non-elastic or partially elasticbefore activating its latent elastic properties.

The term “compound material” refers herein to any material suitable foruse in garments or disposable absorbent articles, which is capable oftransmitting air vapor to provide desired comfort to the wearer.

The term “disposable” is used herein to describe absorbent articles,which generally are not intended to be laundered or otherwise restoredor reused as absorbent articles, but rather discarded after use by thewearer.

The term “breathable” refers herein to any material for use in garmentsor disposable absorbent articles, which is capable of transmitting airvapor to provide desired comfort to the wearer.

Thermoplastic materials suitable for use in the elastomeric compositionsand films of the present technology are generally materials that flowwhen heated sufficiently above their glass transition temperature andbecome solid when cooled.

Thermoplastic materials that have elastomeric properties are typicallycalled elastomeric materials. Thermoplastic elastomeric materials aregenerally defined as materials that exhibit high resilience and lowcreep as though they were covalently crosslinked at ambienttemperatures, yet process like thermoplastic nonelastomers and flow whenheated above their softening point. Thermoplastic elastomeric materials,in particular block copolymers, useful in practicing the presentlydescribed technology can include, for example, linear, radial, star, andtapered block copolymers such as styrene block copolymers, which mayinclude, for example, Kraton® or Kraton®-based styrene block copolymersavailable from Kraton Polymers, Inc., located in Houston, Tex.,styrene-isoprene block copolymers, styrene-(ethylene-butylene) blockcopolymers, styrene-(ethylene-propylene) block copolymers, andstyrene-butadiene block copolymers; polyether esters such as thatavailable under the trade designation HYTREL™ G3548 from E.I. DuPont deNemours; and polyether block amides such PEBAX™ available from ElfAtochem located in Philadelphia, Pa. Preferably, styrene blockcopolymers are utilized in practicing the presently describedtechnology. Styrene-ethylene butylene block copolymers are mostpreferred. The styrene block copolymers of the present technology may beused in the described elastomeric film materials in amounts from about10% to about 50% by weight, based upon the total weight of the film.

Non-styrene block copolymers (elastomers or plastomers) suitable for usein accordance with the presently described technology include, but arenot limited to, ethylene copolymers such as ethylene vinyl acetates,ethylene octane, ethylene butene, and ethylene/propylene copolymer orpropylene copolymer elastomers, such as those available under the tradedesignation VISTAMAXX® available from ExxonMobil, located in Irving,Tex., or ethylene/propylene/diene terpolymer elastomers, and metallocenepolyolefins such as polyethylene, poly (1-hexane), copolymers ofethylene and 1-hexene, and poly(1-octene); thermoplastic elastomericpolyurethanes such as that available under the trade designationMORTHANE™ PE44-203 polyurethane from Morton International, Inc., locatedin Chicago, Ill. and the trade designation ESTANE™ 58237 polyurethanefrom Noveon Corporation, Inc., located in Cleveland, Ohio; polyvinylethers; poly-α-olefin-based thermoplastic elastomeric materials such asthose represented by the formula —(CH2CHR)x where R is an alkyl groupcontaining about 2 to about 10 carbon atoms; poly-α-olefins based onmetallocene catalysis such as ENGAGE™ 8200, ethylene/poly-α-olefincopolymer available from Dow Plastics Co., located in Midland, Mich.;polybutadienes; polybutylenes; polyisobutylenes such as VISTANEX NML-80, available from Exxon Chemical Co.; and polyether block amides suchPEBAX™ available from Elf Atochem located in Philadelphia, Pa. Apreferred elastomer or plastomer of the presently described technologyis an ethylene/propylene copolymer or polypropylene copolymer. It isalso preferable that the non-styrene block copolymer elastomer orplastomer of the presently described technology comprise from about 10%to about 95% by weight of the elastomeric film composition based uponthe total weight of the composition. For example, one embodiment of theelastomer or plastomer of the presently described technology may becomprised of a polypropylene copolymer containing from about 50% toabout 95% of propylene content.

Additional elastomers which can be utilized in accordance with presentlydescribed technology also include, for example, natural rubbers such asCV-60, a controlled viscosity grade of rubber, and SMR-5, a ribbedsmoked sheet rubber; butyl rubbers, such as EXXON™ Butyl 268 availablefrom Exxon Chemical Co., located in Houston, Tex.; syntheticpolyisoprenes such as CARIFLEX™, available from Shell Oil Co., locatedin Houston, Tex., and NATSYN™ 2210, available from Goodyear Tire andRubber Co., located in Akron, Ohio; and styrene-butadiene randomcopolymer rubbers such as AMERIPOL SYNPOL™ 1101 A, available fromAmerican Synpol Co., located in Port Neches, Tex.

Additional thermoplastic materials which may also be useful inpracticing the presently described technology that are generallyconsidered nonelastomeric include, for example, polyolefins such asisotactic polypropylene, low density polyethylene, linear low densitypolyethylene, medium density polyethylene, high density polyethylene,polybutylene, nonelastomeric polyolefin copolymers or terpolymers andblends thereof, ethylene-vinyl acetate copolymers such as thoseavailable under the trade designation ELVAX™ from E. I. DuPont deNemours, Inc., located in Wilmington, Del.; ethylene acrylic acidcopolymers; ethylene methacrylic acid copolymers such as those availableunder the trade designation SURLYN™ 1702 from E.I. DuPont de Nemours,Inc.; polymethylmethacrylate; polystyrene; ethylene vinyl alcohol;polyesters including amorphous polyester; polyamides; fluorinatedthermoplastics such as polyvinylidene fluoride; halogenatedthermoplastics such as chlorinated polyethylene; polyether-block-amidessuch as those available under the trade designation PEBAX™ 5533 fromElf-Atochem North America, Inc., located in Philadelphia, Pa. It will beappreciated by those skilled in the art that these additionalthermoplastic materials may be utilized in accordance with the spiritand scope of the presently described technology to achieve furtherdesired physical properties of the resultant elastomeric compositions orfilms.

It will also be appreciated by those skilled in the art that additivesmay be added to the one or more layers of the presently described filmtechnology in order to improve certain characteristics of the particularlayer. Preferred additives include, but are not limited to, colorconcentrates, neutralizers, process aids, lubricants, stabilizers,hydrocarbon resins, antistatics, and antiblocking agents. It will alsobe appreciated that a color concentrate may be added to yield a coloredlayer, an opaque layer, or a translucent layer. A suitable nucleatingagent may include, for example, calcium carbonate while a suitableprocessing aid may include, for example, calcium stearate.

Suitable antistatic agents may include, for example, substantiallystraight-chain and saturated aliphatic, tertiary amines containing analiphatic radical having from about 10 to about 20 carbon atoms that aresubstituted by ω-hydroxy-(C₁-C₄)-alkyl groups, andN,N-bis-(2-hydroxyethyl)alkylamines having from about 10 to about 20carbon atoms in the alkyl group. Other suitable antistatics can includeethoxylated or propoxylated polydiorganosiloxanes such aspolydialkylsiloxanes and polyalkylphenylsiloxanes, and alkali metalalkanesulfonates.

Antiblocking agents suitable for use with the presently described filmtechnology include, but are not limited to, calcium carbonate, aluminumsilicate, magnesium silicate, calcium phosphate, silicon dioxide, anddiatomaceous earth. Such agents can also include polyamides,polycarbonates, and polyesters.

Additional processing aids that may be used in accordance with thepresently described technology include, for example, higher aliphaticacid esters, higher aliphatic acid amides, metal soaps,polydimethylsiloxanes, and waxes. Conventional processing aids forpolymers of ethylene, propylene, and other α-olefins are preferablyemployed in the present technology. In particular, alkali metalcarbonates, alkaline earth metal carbonates, phenolic stabilizers,alkali metal stearates, and alkaline earth metal stearates arepreferentially used as processing aids for the films of the presentlydescribed technology.

Additional hydrocarbon resins, and in particular, styrene resins,terpene resins, petroleum resins (including polyethylenes andpolypropylenes), nylon resins, ethylene vinyl alcohol resins, andcyclopentadiene resins may also be suitable as additives for use in thedescribed films in order to improve desirable physical properties of thefilms. These properties may include, for example, water vaporpermeability, shrinkage, film rigidity, and optical properties

The multilayer films of the presently described technology may beconstructed of at least two layers, more preferably at least 3 layers,and even more preferably at least 5 layers. The layers may be continuousor discontinuous. The practical upper limit for the number of layerssuitable in the elastomeric film of the presently described technologyis up to about 500.

In a preferred embodiment of the presently described film technologydescribed herein, the film structure is a five-layer structure. Thefive-layer structure allows for a core layer protected by two innerlayers, one positioned on either side of the core layer, and two outerlayers, one positioned on either non-core facing side of each innerlayer. Additionally, the instant five layer structure preferablycomprises the following: HDPE/LDPE outer skin layer (90/10) 5% byweight/VISTAMAXX™ elastomer inner layer 20% by weight/KRATON™ styreneblock copolymer core layer 50% by weight/VISTAMAXX™ elastomer innerlayer 20% by weight/HDPE/LDPE outer skin layer (90/10) 5% by weight,based upon the total weight of the film.

The films of the presently described technology offer a costcompetitive, elastomeric composition capable of being used aselastomeric films, coextruded polymeric film, film laminates, and as acomponent of various articles, such as a disposable absorbent garment(i.e., a nonwoven layer attached to an elastomeric core layer of thepresent technology). Further, the present technology also offers a lowcost elastomeric composition that exhibits improved tear strength andelongation to break, while providing a high elastic recovery, asmeasured by the permanent set, more typical of an expensive SBCelastomeric film.

Again, it has been surprisingly found that the elastomeric films of thepresently described technology have a permanent set substantially equalto or less than an elastomeric film containing one or more layers of SBCalone. As a result, the elastomeric films, laminates, and articles ofthe present technology offer a low cost alternative to more expensiveelastomeric films currently available. Further, the films of the presenttechnology offer good machinability and processability.

In one embodiment, the present technology envisages a laminate having atleast one non-woven layer and at least one elastomeric layer laminatedto the non-woven layer. Such a laminate can be used, for example, inabsorbent products such as disposable undergarments, pants, and the likeor as a component for such articles. The elastomeric film layer of thelaminate preferably comprises at least one styrene block copolymer andat least one elastomer or plastomer which is substantially free ofstyrene block copolymer. Further, the resultant elastomeric film layerhas a permanent set substantially equal to or less than an elastomericfilm layer containing only styrene block copolymer. Moreover, it shouldbe understood by those skilled in the art that the elastomeric filmlayer may be a single layer or may be a multilayer film laminate of onemore layers of styrene block copolymer and one more layers of anelastomer or plastomer substantially free of styrene block copolymer.Additionally, inner and outer skin layering schemes in relation to thecore layer for an elastomeric film multilayer laminate are alsoenvisaged. Moreover, it should be understood that the elastomeric filmsof the presently described technology can have a variety of gauges.Preferably, the gauges of the elastomeric film compositions of thepresent technology range from about 1 mil to about 5 mils.

To make the elastomeric films of the presently described technology, avariety of known film processing techniques (lamination, coextrusion,and the like) may be utilized. In general, a lamination process requiresmultiple steps in which discrete layers of polymer are laminatedtogether to arrive at a finished film. However, it should be understoodby those skilled in the art that the spirit and scope of the presentlydescribed technology envisages the use of a variety of film processingtechniques to arrive at the films described herein.

For example, the multilayer films of the presently described technologymay also be produced via coextrusion. Using this method, melted andplasticized streams of individual layer materials are fed into acoextrusion die. While in the die, the layers are juxtaposed andcombined, after which they emerge from the die in a single multilayerfilm of polymeric material. Further, coextrusion of the films of thepresently described technology may be conducted at temperatures of fromabout 300° F. to about 550° F.

Additionally, coextrusion techniques may include the use of a feed blockwith a standard die, a multi-manifold die, such as a circular die, or amulti-manifold die, such as is used in forming flat cast films and castsheets. The cast film can also be embossed with a texture at the time ofextrusion by dropping the molten film web into a nip between a patternedroll (usually steel) and a non-patterned roll (usually silicone or otherrubber, and if desired, steel). However, it should be understood bythose skilled in the art that the films of the present technology may beembossed or may forego embossing depending upon the type of final filmdesired. Suitable coextrusion techniques for use in producing the filmsof the present technology are fully described in U.S. Pat. Nos.5,139,878 and 4,677,017, which are incorporated by reference in theirentirety. The films of the present technology are preferablymanufactured utilizing a cast process.

The multilayer films of the present technology may also be made viablown film coextrusion. The film is formed using a blown film apparatuscomposed of a multi-manifold circular die head having concentriccircular orifices. The multilayer film is formed by coextruding a moltenlayer through a circular die, and a molten layer on the other or eachopposite side of the first layer through additional circular diesconcentric with the first circular die. Next, a gas, typically air, isblown through a jet that is concentric with the circular dies, therebyforming a bubble that expands the individual layers. The bubble iscollapsed onto itself to form a pair of multilayer films attached at twoopposite edges. Usually, the pair of attached multilayer films are thencut apart at one or more edges and separated into a pair of multilayerfilms that can be rolled up.

All documents, e.g., patents and journal articles, cited above and/orbelow, are hereby incorporated by reference in their entirety. Oneskilled in the art will recognize that modifications may be made in thepresently described technology without deviating from the spirit orscope of the invention. The presently described technology is alsoillustrated by the following examples which are not to be construed aslimiting the invention or scope of the specific procedures orcompositions described herein. All levels and ranges, temperatures,results, etc., used and/or described herein are approximations unlessotherwise specified.

The invention is further illustrated in the following non-limitingExamples. All proportions in the Examples and elsewhere in thespecification are by weight unless specifically stated otherwise.Further, the following examples demonstrate some of the advantages andunique properties of the low cost multi-layer elastic film of thepresently described technology.

Examples Background

Extrusion trials were performed to assess and observe thecharacteristics of films of the presently described technology and forcomparison against conventional films. Kraton styrene block copolymersand ExxonMobil Vistamaxx® ethylene-propylene copolymers were chosen astest materials because both components have among the highest elasticrecovery of commercially available elastomers. They are also the mostwidely used elastic materials in the market today, other than strands.Three layer elastomeric films were developed using each Kraton® (astyrene block copolymer, commercially available from Kraton Polymers,located in Houston, Tex.) and Vistamaxx® (an ethylene/propylenecopolymer, propylene copolymer, or combination thereof, commerciallyavailable from ExxonMobil, located in Irving, Tex.) based resins. In thefilm constructions generated, it is believed the Kraton or Vistamaxxlayer acted as the “elastic engine” which allows for stretch andrecovery properties within the film constructions.

Five layer films were also developed, each film having coextrudedelastic cores comprised of Kraton with Vistamaxx on each side. Table Ibelow shows the basic film compositions. In this situation, the “elasticengine” is the composite of Vistamaxx/Kraton/Vistamaxx. Further, allelastomeric films described herein for the extrusion trials wereextruded with polyolefin skins. The skins were used to provide strengthfor down gauging and to prevent the mechanical film rolls from blockingVistamaxx was extruded with low density polyethylene (“LDPE”) and highdensity polyethylene (“HDPE”) skins, and Kraton was extruded withpolypropylene (“PP”) skins.

Films trials were conducted on cast pilot lines and were run in bothembossed and non-embossed configurations. In embossed operation, theembossing roll was a high-release silicone rubber. Further processingconditions are provided in Table I below.

Test Method

Due to the films being tested having polyolefin skins, the filmsrequired “activation” before the film can act as an elastomer. Forinformation regarding “activation” of films, see U.S. Pat. No.5,691,034, which is incorporated by reference herein in its entirety. Ingeneral, activation involves stretching the film to a strain of at least200%. Commercially, the “activation” of a film will occur on commercialfilm production line, usually during lamination. However, “activation”can be simulated in the laboratory utilizing a multi-cycle tensilehysteresis test. For the extrusion trials discussed herein, the firstcycle served as the “activation” cycle.

Tensile hysteresis tests were done using an Instron mechanical tester.Samples strips were cut to a size of 1 inch×4 inches with a gauge lengthof 2 inches. The films were extended to an extension of 6 inches (300%strain) and then unloaded to 0 inches at a crosshead speed of 10inches/minute. This was done for two complete cycles.

Results Physical Properties Observed

First cycle hysteresis curves are shown in FIG. 1 below for Kraton andVistamaxx. The permanent set on the first cycle controls the maximumelongation of the film in use on an absorbent product. In FIG. 1, Kratonhad a lower permanent set after the first cycle, which means anabsorbent product made with Kraton will have a larger maximum elongationcompared to Vistamaxx for a given strain.

FIG. 2 below shows a second cycle loading curve of Vistamaxx and Kratonfilms at similar gauges, in a range from about 1 to about 5 mils. Bothelastic resins provided similar force at equivalent gauge. Further, theskin resin appeared to have minimal or no effect on the force curves.The skin resins for the film samples were PP for Kraton and LDPE forVistamaxx. FIG. 2 shows that the “elastic engine” controls the loadingforces for the three layer films tested.

FIG. 3 below shows Kraton MD6932 and G1657 second cycle hysteresiscurves overlaid at a gauge of 5 mils. Additionally, FIG. 4 below showsVistamaxx 1100 and 1120 second cycle hysteresis curves overlaid at agauge of 1.5 mils. In both cases, there is minimal or no differencebetween the elastomers, which are from the same chemical family. Itshould be noted and appreciated by those skilled in the art, however,that there is a large difference in the set between FIGS. 3 and 4, aswould be expected between these two chemical families.

FIG. 5 below shows the effect of skin resin type on Vistamaxx VM1120.The second cycle hysteresis curve is given for VM1120 with LDPE and HDPEskins. The film with HDPE provided a slightly higher force compared withLDPE, but the permanent set was unaffected. Such a result as provided inFIG. 5 indicates that the Vistamaxx layer is controlling the permanentset outcome of the produced films. Further, second cycle permanent setdata is provided for in FIG. 6 below for VM1120 films. As can be seen inFIG. 6, the set is relatively unaffected by film thickness. However,decreasing the skin percentage from 10% to 5% reduced the permanent setslightly.

The effect of skin layer ratio was also examined for the Vistamaxxfilms. The loading force after activation is shown for VM1120 at 2 and 3mil gauge with total skin percentages of 5 and 10% is shown in FIG. 7below. At lower strains (<100%), the skin percentage had a minimaleffect, again showing the ability of the Vistamaxx layer to act as an“elastic engine” control for elastomeric film or material. At higherstrains, the higher skin percentage requires higher force to continueelongation.

An overlay of Kraton G1657 and Vistamaxx VM1120 is shown in FIG. 8below. It should be noted and appreciated by those skilled in the artthat Kraton has much lower force at higher strain as compared toVistamaxx. Additionally, the permanent set for Kraton is about half ofthe permanent set for that of Vistamaxx. Such an outcome as illustratedin FIG. 8 demonstrates that the “elastic engine” controls the stretchand recovery properties of the three layer film produced. A five layerstructure containing a coextruded elastic core is also shown in FIG. 8.The core is a three layer coextrusion having Kraton MD6932 in the centerwith Vistamaxx VM1100 on either side. This film has HDPE skins (seeTable I below).

The permanent set for the three films of FIG. 8 is provided in FIG. 9below. Surprisingly, the five layer film has a permanent set similar tothat of pure Kraton film rather than that of a pure Vistamaxx film,despite both elastomers being present in the structure. It will beappreciated by those skilled in the art that multiple resin films suchas a coextrusion of Vistamaxx and Kraton, in general, will generateresultant physical properties which are an average of the two separateelastomers' physical properties. Surprisingly, this result did not occurwith respect to permanent set utilizing the films of the presenttechnology as illustrated in FIGS. 8 and 9. As observed, the five layerfilm had the advantage of providing a low force to extend and lowpermanent set, while providing a higher elongation to break and TD tearstrength than a film of Kraton alone could provide.

The elongation to break and Elmendorf tear strength data are given belowin FIGS. 10 and 11, respectively. The graphs of FIGS. 10 and 11illustrate that the properties of the five layer structure are anaverage of the properties of the two elastomers. As noted above, thisoutcome is typically expected in coextruded structures.

Discussion

Extrusion trials with three layer Kraton-containing films demonstratedthat an A/B/A structure with 8 percent total skins (5/90/5) allowed thefilms to be extruded and down gauged with standard processingconditions.

With 10% total HDPE skins, Vistamaxx resins were able to be down gaugedto 1.25 mils. The higher melt strength of Vistamaxx also allowed forreducing the skins to 5% (2.5/95/2.5). Further, the five layerstructures using both Vistamaxx and Kraton had the following structure:HDPE/LDPE (90/10) 5%/Vistamaxx 20%/Kraton 50%/Vistamaxx 20%/HDPE/LDPE(90/10) 5%. It was observed that such five layer films were able to bedown gauged to 1.25 mils during standard processing. In this respect,the Vistamaxx melt strength enhanced the properties of the five layerstructure. This result is surprising given the presence of a Kratoncentral layer. Although not wanting to be bound by any particulartheory, it is believed the inclusion or incorporation of an elastomer orplastomer such as ethylene/propylene copolymer, propylene copolymer, orcombination thereof, with a styrene block copolymer can result in anelastomeric film having a permanent set substantially equal to or lessthan an elastomeric film containing styrene block copolymer only. Inaddition, the five layer structure as discussed above (see FIGS. 8-11below) with two elastomers has the further advantage, as mentionedpreviously, of processability and down gauging to lower film thickness.

TABLE I Film Structures Layers Elastic Core Elastic Resin Grades SkinResin 3 ExxonMobil VM1100 HDPE “Vistamaxx ®” VM1120 LDPE, HDPE 3 KratonPolymers MD6932 PP “Kraton ®” G1657 PP 5 VM/Kraton/VMVM1120/MD6932/VM1120 HDPE VM1100/G1657/VM1100 HDPE

TABLE II Processing Temperatures for Elastic Films (° F.) KratonVistamaxx Barrel Zone 1 370 300 Barrel Zone 2 390 330 Barrel Zone 3 420350 Barrel Zone 4 420 370 Barrel Zone 5 420 400 Die Zone (1-5) 420 400Melt Temp 1 435 400 Melt Temp 2 415 400 Chill Roll Temp 50-55 50-55 *Temps in ° F.

TABLE III Description of films of the presently described technology.Permanent Set Elastic Core Resin Gauge (mil) Cycle 1 Cycle 2 G1657 1.530.0% 5.8% VM1120 1.5 75.0% 16.0% VM1100 1.5 50.0% 13.6% VM1100 1.2553.0% 13.3% VM1100/G1657/VM1100 1.5 40.0% 8.1% VM1120/MD6932/VM1120 1.541.0% 6.7% VM1120/MD6932/VM1120 1.25 42.0% 7.8%

The presently described technology and the manner and process of makingand using it, are now described in such full, clear, concise and exactterms as to enable one of ordinary skill in the art to which the presenttechnology pertains, to make and use the same. It should be understoodthat the foregoing describes some embodiments and advantages of theinvention and that modifications may be made therein without departingfrom the spirit and scope of the presently described technology as setforth in the claims. Moreover, the invention has been described withreference to preferred and alternate embodiments. Modifications andalterations will occur to others upon the reading and understanding ofthe specification. It is intended to include all such modifications andalterations insofar as they come within the scope of the appended claimsor equivalents thereof. To particularly point out and distinctly claimsthe subject matter regarded as the invention, the following claimsconclude this specification.

1. An elastomeric composition comprising: at least one styrene blockcopolymer; and at least one elastomer or plastomer which issubstantially free of styrene block copolymer, and wherein theelastomeric composition has a permanent set substantially equal to orless than an elastomeric composition containing only styrene blockcopolymer.
 2. The elastomeric composition of claim 1, wherein theelastomer or plastomer is a thermoplastic polyolefin, thermoplasticpolyurethane, or polyvinyl ether.
 3. The elastomeric composition ofclaim 2, wherein the thermoplastic polyolefin is a member selected fromthe group consisting essentially of: ethylene copolymers,ethylene/poly-α-olefin copolymers, an amino-compatibilized polyolefin, ablend of ethylene/poly-α-olefin and amino-compatibilized polyolefinethylene/propylene copolymers, ethylene/propylene/diene terpolymers,metallocene polyolefin, combinations thereof, or derivatives thereof. 4.The elastomeric composition of claim 1, wherein the elastomer ofplastomer is an ethylene/propylene copolymer or a polypropylenecopolymer.
 5. The elastomeric composition of claim 1, wherein thecomposition further comprises at least one additive selected from thegroup consisting of: color concentrates, process aids, lubricants,stabilizers, hydrocarbon resins, antistatics, viscosity reducingpolymers, plasticizers, antioxidants, bonding aids, slip agents, heatstabilizers, photostabilizers, glass bubbles, micro fibers, andantiblocking agents.
 6. A method of manufacturing a multilayerelastomeric film, the method comprising the step of: coextruding atleast one styrene block copolymer layer with at least one elastomer orplastomer layer substantially free of styrene block copolymer, whereinthe resultant multilayer elastomeric film has a permanent setsubstantially equal to or less than that of a coextruded multilayerelastomeric film containing one or more layers of styrene blockcopolymer only.
 7. The method of claim 6, wherein the method furthercomprises the step of providing an additive for inclusion with orincorporation into the film.
 8. The method of claim 7, wherein theadditive is a member selected from the group consisting of: colorconcentrates, neutralizers, process aids, lubricants, stabilizers,hydrocarbon resins, antistatics, viscosity reducing polymers,plasticizers, antioxidants, bonding aids, slip agents, heat stabilizers,photostabilizers, glass bubbles, microfibers, and antiblocking agents.9. The method of claim 6, wherein the elastomer or plastomer layercomprises a thermoplastic polyolefin, a thermoplastic polyurethane, or apolyvinyl ether, a combination thereof, or a derivative thereof.
 10. Themethod of claim 6, wherein the elastomer or plastomer layer is anethylene/propylene copolymer or polypropylene copolymer.
 11. The methodof claim 6, wherein the method further includes the step of casting themultilayer elastomeric film.
 12. The method of claim 6, wherein themethod further includes the step of cast embossing the multilayerelastomeric film.
 13. An elastomeric product produced in accordance withthe process as set forth in claim
 6. 14. A method of manufacturing amultilayer elastomeric film, the method comprising the steps of:providing at least one core layer consisting of a styrene blockcopolymer; and providing at least two outer layers comprising anon-styrene block elastomer or plastomer, and wherein the resultantmultilayer elastomeric film has a permanent set substantially equal toor less than the permanent set of a multilayer elastomeric filmconsisting only of styrene block copolymer.
 15. The method of claim 14,wherein the method further comprises the step of providing an additive.16. The method of claim 14, wherein the non-styrene block elastomer orplastomer is an ethylene/propylene copolymer or propylene copolymer. 17.An elastomeric product produced in accordance with the process as setforth in claim
 14. 18. A method of manufacturing a multilayerelastomeric film laminate, the method comprising the step of: laminatingat least one styrene block copolymer layer with at least one elastomeror plastomer layer, wherein the resultant multilayer elastomeric filmlaminate has a permanent set substantially equal to or less than that ofa multilayer elastomeric film laminate containing only one or morelayers of styrene block copolymer.
 19. An elastomeric product producedin accordance with the process as set forth in claim
 18. 20. A componentfor an absorbent article comprising: at least one non-woven outer layer;and at least one elastomeric film inner layer attached to the non-wovenouter layer, and wherein the elastomeric film inner layer comprises: atleast one layer comprising a styrene block copolymer; and at least onelayer consisting essentially of an elastomer or plastomer, and whereinthe elastomeric film inner layer has a permanent set substantially equalto or less than an absorbent article containing an elastomeric filminner layer comprised only of styrene block copolymer.